Renewable Energy Technology Assessments - Kauai Island Utility ...

Kaua’i Island Utility Cooperative
Renewable Energy Technology Assessments
3.0 Renewable Energy Technology
Options
part of the cell production cost. Other methods of crystalline cell production (casting of
polycrystalline material, pulling of cell-thickness ribbons) can cut material costs at some
penalty to cell efficiency.
Another approach to reducing cell material cost is the development of thin film
PV cells. Commercial thin films are principally made from amorphous silicon; however,
amorphous silicon cells suffer significant degradation and are not being seriously
developed for large power applications. Copper indium diselenide and cadmium telluride
show promise as low-cost solar cells. Thin film solar cells require very little material and
can be manufactured on a large scale. Furthermore, the fabricated cells can be flexibly
sized and incorporated into building components. However, to date, thin film technology
has not proven to be cost effective compared to crystalline silicon.
Gallium arsenide cells are among the most efficient solar cells and have other
technical advantages, but they are also more costly. Gallium arsenide cells are typically
used where high efficiency is required even at a high cost, such as space applications.
Applications
The modularity, simple operation, and low maintenance requirements of solar PV
makes it ideal for serving distributed, remote, and off-grid applications. Most PV
applications are smaller than 1 kW, although, larger utility-scale installations are
becoming more prevalent. Current grid-connected PV systems are generally below 100
kW. Several larger projects ranging from 1 to 50 MW have been proposed. A 3.4 MW
project is under construction in Arizona. This is one of the largest PV installations in the
world. Most grid-connected PV applications require large subsidies (50 percent or more)
to overcome inherently high initial costs.
Resource Availability
Solar radiation reaching the earth’s surface, often called insolation, has two
components: direct normal insolation (DNI) and diffuse insolation. DNI, which
comprises about 80 percent of the total insolation, is that part of the radiation which
comes directly from the sun. Diffuse insolation is that part of the radiation which has
been scattered by the atmosphere or is reflected off the ground or other surfaces. All of
the radiation on a cloudy day is diffuse. The vector sum of DNI and diffuse radiation is
termed global insolation. Systems which concentrate solar energy use only DNI, while
non-concentrating systems use global radiation. Most PV systems installed today are flat
plate systems that use global insolation. Concentrating PV systems, which use DNI, are
being developed, but are not considered commercial at this time.
39 Paul Maycock, “PV market update”, Renewable Energy World, July-August 2003.
21 March 2005 3-59 Black & Veatch